Video signals generally include data corresponding to one or more video frames, where each video frame is composed of an array of picture elements (pixels). A typical color video frame at standard resolution can be composed of over several hundred thousand pixels arranged in an array of blocks. Each pixel is typically characterized with a color (or hue) and luminance characteristics. Thus, digital signals representing a sequence of video frames have a large number of bits. However, the available storage space and bandwidth for transmitting such signals is limited. Therefore, compression processes are used to more efficiently transmit or store video data.
One type of compression technique is the MPEG-4 Part 10 compression (referred to herein as MPEG-4). MPEG-4 is the same as the H.264 standard. These standards, which are identical, are maintained by the ITU and MPEG standards organizations and include both field and frame coding.
Prior to compressing a frame, typically the characteristics or content of the frame is determined. Complexity may be used as a measure of the characteristics or content of the picture or frame. For example, a pure black or a pure white frame has low complexity at least because there is little or no difference between pixels in the frame. Complexity is used to estimate the number of bits per frame. A higher complexity means more bits are needed to represent data in the frame. It is standard to budget a number of bits per frame. Then, during coding, the encoder tries to meet that bit budget per frame. If the budget is exceeded, it may cause overflow of a video buffering verifier, which is a model hypothetical decoder buffer used in MPEG-4. Then, the next frame will have to take away bits, which can results in video degradation.
Special events, such as scene changes, may result in consecutive frames having substantially different images. Conventional encoders may base complexity of a frame solely on the complexity of the previous frame. However, if the consecutive frames are substantially different, such as due to a scene change or other special event, then the complexity determination becomes inaccurate. This can lead to video breaks or other video degradation.